1. Field of the Invention
The present invention relates to a wired circuit board and to a production method thereof. More particularly, the present invention relates to a wired circuit board having terminals connected to external terminals and to a production method of the same.
2. Description of the Prior Art
The wired circuit board commonly comprises a conductive pattern comprising a plurality of wires formed on an insulating base layer, and an insulating cover layer formed on the insulating base layer for covering the conductive pattern.
In this wired circuit board, the conductive pattern has terminal portions for connecting to external terminals of an electronic component and the like, and the insulating cover layer has an opening formed correspondingly for the terminal portions. The terminal portions are exposed from the opening for connecting with the external terminals.
For example, a flip-chip-mounting printed circuit board comprising a board body forming a board conductor thereon, and an insulating protection film formed on the board body and having an opening at a location where an IC chip is mounted has been proposed as the wired circuit board, wherein a connection conductor portion of the board conductor is exposed from the opening so that it can connect with electrodes of the IC chip (Cf. Japanese Unexamined Patent Publication No. 2005-175113, for example).
In this wired circuit board, relative arrangement between the terminal portions and the opening, and a dimension of the opening are critical for the reliable connection between the terminal portions and the external terminals.
Several methods for forming the opening in the insulating cover layer are known: a first method of a photo processing method using a photo mask via which a photosensitive resin is exposed to light and developed to form the opening in the insulating cover layer; a second method of a printing method using a solder resist for forming the opening in the insulating cover layer; and a third method that an insulating resin film having an opening previously formed is adhesively bonded to form the insulating cover layer, or after an insulating resin film having no opening is adhesively bonded via an adhesive to form the insulating cover layer, an opening is formed in the insulating cover layer.
However, any of the first to third methods outlined above has a possible problem that an actual position of the opening formed may be displaced from a designed position of the opening.
Specifically, the first method has a possible problem that due to possible displacement of the photo mask in the photo process, the actual position of the opening formed may be displaced from the designed position of the opening. The second method has a possible problem that due to possible pattern misalignment that may be caused by displacement of the solder resist in the printing process, the actual position of the opening formed may be displaced from the designed position of the opening, or an actual dimension of the opening formed is deviated from the designed dimension of the opening. Further, the third method involves possible problems that the insulating resin film having the opening previously formed may be adhesively bonded with the opening displaced from the designed position, that the insulating resin film may be bored after bonding at a position displaced from the designed position of the opening of the insulating resin film, and that the opening may be bored with its actual dimension deviated from the designed dimension of the opening.
If the actual position of the opening formed is displaced from the designed position of the opening, then the terminal portions are covered with the insulating cover layer, in other words, is exposed so insufficiently that an electronic component cannot be mounted, so that it causes difficulties in mounting the electronic component reliably. Accordingly, in the production method of this wired circuit board, determination must be made whether or not the actual position of the opening formed in the insulating cover layer is displaced from the designed position of the opening. If the actual position of the opening formed in the insulating cover layer is determined displaced from the designed position of the opening, the wired circuit board must be removed as a defective product.
The displacement of the relative position between the terminal portions and the opening, and the dimensional deviation of the opening formed can be determined by actual measurement using a microscope, for example, which is known as a method for determining whether or not the actual position of the opening formed in the insulating cover layer is displaced from the designed position of the opening.
However, this known measuring method takes a lot of troubles with the determination of the displacement, and thus have difficulties in realizing cost reduction while ensuring high productivity.